Following the Moore's law, the semiconductor industry is constantly willing to shrink the chip size in order to increase its performance. In order to do so, the power metal of the semiconductor is required to offer a high electrical and thermal conductivity. Hence, copper is conventionally used as the power metal. However, copper belongs to the category of noble metals and thus lacks a pertinent native oxide layer which obstructs the further diffusion of oxygen into the bulk copper. This leads to several problems such as copper oxidation, delamination, and loss of at least one of a electrical or thermal conductivity. Therefore, an oxide layer which does not allow the diffusion of the oxygen into copper film and thereby oxidizing it is required on the copper film. At present stage, no optimal solution is available to solve those problems. In a conventional method, a thin layer of alumina having a thickness of a few nanometers is deposited on the copper film using an atomic layer deposition (ALD) process. The alumina film formed by ALD is thick enough to insulate the copper against its oxidation and at a same time thin enough for the post bonding processes. A disadvantage of this method is that the ALD process is surface sensitive and also sensitive to the orientation of the copper grains. At the same time, the adhesion of the ALD deposited alumina film is usually not strong enough on the copper film. This leads to the delamination of the alumina film during post processing e.g. in packaging. In addition, ALD needs capital investment. Further, the repetitive pulsed ALD process makes the forming of the alumina layer time ineffective and may lead to high production cost.
Moreover, copper strongly reacts with the semiconductor substrate under the marginal of thermal and electrical budget (thermo/electro-immigration). Therefore, a barrier is required that separates the substrate and copper physically without or minimally influencing the electrical performance of the device. Metal oxides Al2O3 and MnO2 are known to function as a copper barrier. The alloy of that metal with copper is commonly sputter deposited on the substrate and with thermal budget the alloying metal is diffused out of the alloy to form its oxide at the interface (self forming barrier). However, this technique is not suitable for forming a barrier layer in contact holes of the semiconductor device with relatively high aspect ratios. Further, the required oxygen for the oxide formation of the barrier layer is taken from the SiO2 or from native oxide of the silicon substrate of the semiconductor. Thus, this method is usually not suitable in frequently used devices in which copper alloy is deposited directly on the surface of the silicon substrate without native silicon oxide layer. Further problems of conventional copper barrier materials are the adhesion of copper on the barrier layer, the influence of the barrier on the electrical performance, the cost effectiveness and ease of processing, e.g. the depositing and structuring of the barrier layer.